Molecular basis of macrolide-lincosamide-streptogramin (MLS) resistance in Finegoldia magna clinical isolates.

Of 69 clinical isolates of Finegoldia magna tested, 36% presented high-level MICs of erythromycin (>256 µg/ml), harboring erm(A) (n = 20) or erm(B) (n=5). Of nine isolates exhibiting an inducible resistance phenotype to macrolides-lincosamides-streptogramins B, four (44%) were susceptible with a potential risk of treatment failure due to emergence of resistant mutants.

Phenotypic and genotypic characterization of macrolide resistance among Staphylococcus aureus isolates in Isfahan, Iran.

BACKGROUND AND OBJECTIVES: Macrolide, lincosamide and streptogramin B (MLS B) are noteworthy antibiotics for the treatment of Staphylococcus aureus infections. The purpose of this study, was to determine the phenotypic and genotypic characterization of macrolide resistance, among S. aureus, isolated from clinical samples and nasal swabs. MATERIALS AND METHODS: Totally, 162 non-duplicate S. aureus isolates were collected from clinical samples and nasal swabs, from patients and healthcare workers (HCWs), between March 2016 and September 2016, at four teaching hospitals in Isfahan. The antibiotic resistance profile was determined using disk diffusion test and the presence of resistance genes was detected, using PCR. RESULTS: Of 162 S. aureus isolates, 43.8% (71/162) and 34% (55/162) isolates were erythromycin-resistant and methicillin-resistant S. aureus (MRSA), respectively. The prevalence of constitutive MLS B (cMLS B), inducible MLS B (iMLS B), macrolide-streptogramin B-resistant (MS B) and lincosamide-streptogramin-A resistance (LS A) phenotype was 32%, 6%, 6% and 2%, respectively. The most common erythromycin resistance genes, in S. aureus isolates were ermC (35.2%), followed by ermA (20.4%) and msrA (17.3%). Meanwhile, msrA was detected in 43.6% of MRSA isolates. The frequency of coexistence of ermA+ermC+msrA, in S. aureus isolates was 7% and it was only detected in MRSA isolates. CONCLUSION: In the current study, cMLS B phenotype was the most common erythromycin resistance pattern and ermC was the most prevalent gene in erythromycin-resistant isolates. The results revealed that the various mechanisms of erythromycin resistance are expanding in Isfahan.

Frequency of genes encoding erythromycin ribosomal methylases among Staphylococcus aureus clinical isolates with different D-phenotypes in Tehran, Iran.

BACKGROUND AND OBJECTIVES: Macrolide, lincosamide and streptogramin type B (MLSB) antibiotics are important in the treatment of Staphylococcus aureus infections and existence of isolates with ability to resist against MLSB antibiotics is worrisome. MATERIALS AND METHODS: In this cross sectional study, 101 S. aureus isolates were collected from patients of five selected hospitals in Tehran over a period of five months. Disk diffusion tests and differentiation between constitutive and inducible resistances were carried out by D-test. The presence of mecA, msrA, ermA and ermC genes were detected using PCR or multiplex PCR. RESULTS: Out of 101 S. aureus isolates, 58 (57.4%) were methicillin resistant and 57 (56.4%) expressed resistance to erythromycin. The prevalence of constitutive MLSB (cMLSB), inducible MLSB (iMLSB) and MS (Negative) phenotype in all erythromycin resistant isolates were 71.9, 26.3 and 1.7%, respectively. Out of all the erythromycin resistant isolates, 57.8% harbored both ermA and ermC genes which possessed constitutive resistance. 8.7% of the isolates contained ermA gene alone which possessed inducible resistance with D phenotype and 5.2% of isolates just contained ermC gene which had inducible resistance with D+ phenotype. msrA gene was detected in 3.5% of the erythromycin resistant S. aureus isolates with constitutive resistance. None of the genes were detected among MS phenotypes. CONCLUSION: In this study, most of S. aureus isolates carried both ermA and ermC genes and there was a significant relationship (P value ≤ 0.05) between different resistance phenotypes and erm genes.

Quantification of lincomycin resistance genes associated with lincomycin residues in waters and soils adjacent to representative swine farms in China.

Lincomycin is commonly used on swine farms for growth promotion as well as disease treatment and control. Consequently, lincomycin may accumulate in the environment adjacent to the swine farms in many ways, thereby influencing antibiotic resistance in the environment. Levels of lincomycin-resistance genes and lincomycin residues in water and soil samples collected from multiple sites near wastewater discharge areas were investigated in this study. Sixteen lincomycin-resistance and 16S rRNA genes were detected using real-time PCR. Three genes, lnu(F), erm(A), and erm(B), were detected in all water and soil samples except control samples. Lincomycin residues were determined by rapid resolution liquid chromatography-tandem mass spectrometry, with concentrations detected as high as 9.29 ng/mL in water and 0.97 ng/g in soil. A gradual reduction in the levels of lincomycin-resistance genes and lincomycin residues in the waters and soils were detected from multiple sites along the path of wastewater discharging to the surrounding environment from the swine farms. Significant correlations were found between levels of lincomycin-resistance genes in paired water and soil samples (r = 0.885, p = 0.019), and between lincomycin-resistance genes and lincomycin residues (r = 0.975, p < 0.01). This study emphasized the potential risk of dissemination of lincomycin-resistance genes such as lnu(F), erm(A), and erm(B), associated with lincomycin residues in surrounding environments adjacent to swine farms.

pDB2011, a 7.6 kb multidrug resistance plasmid from Listeria innocua replicating in Gram-positive and Gram-negative hosts.

pDB2011, a multidrug resistance plasmid isolated from the foodborne Listeria innocua strain TTS-2011 was sequenced and characterized. Sequence analysis revealed that pDB2011 had a length of 7641 bp and contained seven coding DNA sequences of which two were annotated as replication proteins, one as a recombination/mobilization protein and one as a transposase. Furthermore, pDB2011 harbored the trimethoprim, spectinomycin and macrolide-lincosamide-streptogramin B resistance genes dfrD, spc and erm(A), respectively. However, pDB2011 was only associated with trimethoprim and spectinomycin resistance phenotypes and not with phenotypic resistance to erythromycin. A region of the plasmid encoding the resistance genes spc and erm(A) plus the transposase was highly similar to Staphylococcus aureus transposon Tn554. The dfrD gene was 100% identical to dfrD found in a number of Listeria monocytogenes isolates. Additionally, assessment of the potential host range of pDB2011 revealed that the plasmid was able to replicate in Lactococcus lactis subsp. cremoris MG1363 as well as in Escherichia coli MC1061 and DH5α. This study reports the first multidrug resistance plasmid in L. innocua. A large potential for dissemination of pDB2011 is indicated by its host range of both Gram-positive and Gram-negative bacteria.

Macrolide Resistance in beta-Hemolytic Streptococci: Changes after the Implementation of the Separation of Prescribing and Dispensing of Medications Policy in Korea

This study evaluated the antimicrobial susceptibilities and macrolide resistance mechanisms of beta-hemolytic streptococci (BHS), and an additional objective was to assess the effects of 'the separation of prescribing and dispensing (SPD) of medications' on bacterial resistance rate and distribution of phenotypes and genotypes of erythromycin-resistant BHS by comparing the antimicrobial susceptibility data before (1990- 2000) and after the implementation of SPD at one tertiary care hospital in South Korea. Between the period of January 2001 and December 2002, the minimal inhibitory concentrations of six antimicrobials were determined for 249 clinical isolates of BHS. Resistance mechanisms of erythromycin-resistant (intermediate and resistant) isolates were studied by using the double disk test and PCR. Overall, the resistance rates to tetracycline, erythromycin, and clindamycin were 75.5%, 32.9%, and 32.5%, respectively. Sixty-seven (81.7%) of 82 erythromycin- resistant isolates expressed constitutive resistance to macrolide- lincosamide-streptogramin B antibiotics (a constitutive MLSB phenotype) ; 11 isolates (13.4%) expressed an M phenotype; and four isolates (4.9%) had an inducible MLSB resistance phenotype. erm (A) was found in isolates with constitutive/ inducible MLSB phenotypes, erm (B) with the constitutive/ inducible MLSB phenotype, and mef (A) with the M phenotype. We found that resistance rates to erythromycin and clindamycin among S. agalactiae, S. pyogenes, and group C streptococci isolates were still high after the implementation of the SPD policy in Korea, and that the constitutive MLSB resistance phenotype was dominant among erythromycin- resistant BHS in this Korean hospital.

Distributions of Macrolide-Lincosamide-Streptogramin (MLS) Resistance Types in beta-hemolytic Streptococci / 대한임상미생물학회지

BACKGROUND: Macrolide resistance in beta-hemolytic streptococci has increased during the 1990s, and the proportion of MLS (Macrolide-lincosamide-streptogramin) resistance phenotypes and genotypes of beta-hemolytic streptococci are quite different by geographical variation and study period. The aim of the present study was to determine the distribution of MLS resistance phenotypes and genotypes in beta-hemolytic streptococci isolated from Wonju Christian Hospital. METHODS: The minimal inhibitory concentrations of erythromycin and clindamycin of 426 beta- hemolytic streptococci isolated from clinical specimens between 1990 to 1999 were determined by agar dilution method. MLS resistance phenotypes were determined by double disk diffusion method using erythromycin and clindamycin disk, and genotypes were determined by polymerase chain reaction (PCR). The PCR primers for erm(A), erm(B), erm(C), erm(TR), and mef(A) were used in these study. RESULTS: The proportion of MLS resistance phenotypes of 80 erythromycin-resistant beta-hemolytic streptococci were 60.0% for constitutive phenotype, 23.8% for M phenotype, and 16.2% for inducible phenotype. The proportion of three MLS resistance phenotypes of group A streptococci were nearly equal. About three-fourths of group B streptococci had the constitutive phenotypes, whereas three-fourths (75%) of group G streptococci had the M phenotypes. All MLS resistant strains carried the erm(B) genes in constitutive phenotypes, erm(TR) genes in inducible phenotypes, and mef(A) genes in M phenotypes, respectively. CONCLUSIONS: Mechanisms and phenotype proportions of MLS resistance are different by species in beta-hemolytic streptococci. It is possible that MLS resistance genes have transferred among beta- hemolytic streptococci because the erythromycin resistance genes are the same in beta-hemolytic streptococci.